A storage system is a processing system adapted to store and retrieve data on storage devices (such as disks). The storage system includes a storage operating system that implements a file system to logically organize the data as a hierarchical structure of directories and files on the storage devices. Each file may be implemented as a set of blocks configured to store data (such as text), whereas each directory may be implemented as a specially-formatted file in which data about other files and directories are stored. The storage operating system may assign/associate a unique storage system address (e.g., logical block number (LBN)) for each data block stored in the storage system.
The storage operating system generally refers to the computer-executable code operable on a storage system that manages data access and access requests (read or write requests requiring input/output operations) and may implement file system semantics in implementations involving storage systems. In this sense, the Data ONTAP® storage operating system, available from NetApp, Inc. of Sunnyvale, Calif., which implements a Write Anywhere File Layout (WAFL®) file system, is an example of such a storage operating system implemented as a microkernel within an overall protocol stack and associated storage. The storage operating system can also be implemented as an application program operating over a general-purpose operating system, such as UNIX® or Windows®, or as a general-purpose operating system with configurable functionality, which is configured for storage applications as described herein.
A storage system's storage is typically implemented as one or more storage volumes that comprise physical storage devices, defining an overall logical arrangement of storage space. Available storage system implementations can serve a large number of discrete volumes. A storage volume is “loaded” in the storage system by copying the logical organization of the volume's files, data, and directories, into the storage system's memory. Once a volume has been loaded in memory, the volume may be “mounted” by one or more users, applications, devices, and the like, that are permitted to access its contents and navigate its namespace.
A storage system may be configured to allow server systems to access its contents, for example, to read or write data to the storage system. A server system may execute an application that “connects” to the storage system over a computer network, such as a shared local area network (LAN), wide area network (WAN), or virtual private network (VPN) implemented over a public network such as the Internet. The application executing on the server system may send an access request (read or write request) to the storage system for accessing particular data stored on the storage system.
The storage system may typically implement large capacity disk devices for storing large amounts of data. In conjunction with the large capacity disk devices, the storage system may also store data on other storage devices, such as low-latency random read memory (referred to herein as “LLRRM”). When using LLRRM devices in conjunction with disk devices to store data, the storage system may map storage system addresses (e.g., LBNs) to LLRRM addresses to access data on the LLRRM devices. Typically, the storage system implements direct remapping of storage system addresses to LLRRM addresses whereby a single remapping table is used to list storage system addresses and their corresponding LLRRM addresses.
Conventional direct remapping methods are simple in implementation and sufficient for LLRRM devices having relatively small storage capacities. Conventional direct remapping methods, however, become difficult to maintain with LLRRM devices having relatively large storage capacities as the size of the single remapping table (due to the direct mapping nature) become too large to manage efficiently. As such, there is a need for a method and apparatus for remapping addresses on large capacity low-latency random read memory.